Lightning arrester



Patented May 22, 1951 LIGHTNING ARRESTER' Stanislas Teszner, Paris,France, assignor to Forges et Ateliers de Constructions'Electriques deJeumont, Paris, France, a French body cor-' porate Application March 23,1948,.SerialNo. 16,593 In France March 26, 1947 Claims.

The present invention relates to lightning arresters comprisingessentially an assembly of arc or spark gaps in series with resistances.Special resistances made of valve-type material, which vary in inverseratio to the voltage, have enabled very considerable progress to be madein the arrester characteristics and performance; on the other hand, theadvance in spark gap designhas hitherto been less marked.

These spark gaps have to fulfil in particular the following conditions:

(1) To present an adequate breaking power for the interruption of' theresidual current traversing the resistances; and to ensure the stoppageof this current within a short time, of the order of a half-period.at'the most.

(2) To withstand without considerable erosion theresidual current aswell as the surge currents, up to the nominal discharge power of thearrestor.

(3) To possess, especially withrespect to high frequency or surge waves,a relatively low striking voltage, and, despite this, to present arelatively high breaking voltage at industrial frequencies, withoutallowing any leakage current.

(4) To be of simple, cheap and compact construction.

Lightning arresters knownat' the present day do not fulfil all theseconditions in a sufficient degree, and the present invention has for itsmain object to solve the problem thus set. Likewise and in a moregeneral way, it has" for another object the provision of improvedlightning arresters suitable for medium and high voltages.

A specific object of the invention is the provision of an improvedlightning arrester comprising a series of adjustable spark gaps,provided with simple means for magnetic blow-out in a field excited bythe current, as well as means for ensuring the optimum distribution ofpotential over the said spark gaps by the intermediary of suitablecapacitances associated with high resistances and constituting a chainin which, at low frequencies, the distribution is essentially determinedby the said capacitances, with no current flowing through theresistances, while during the transitory phenomena at high surgefrequencies, it is essentially determined by the said resistances and bythe capacitances with respect to ground.

Due to this, there is obtained, particularly at in-' dustrialfrequencies, uniform voltage distribution facilitating the obtaining ofa relatively high breaking voltage, while for steep-fronted waves, thereis obtained a non-uniform distribution which lowers substantially thestriking voltage in relation to that which corresponds to industrialfrequencies.

Other objects and advantages of the invention Will appear from thefollowing description given 2. with reference to the accompanyingdrawings of an embodiment of a" lightning arrester designed for amoderate voltage of theorder of 7 kv. for example.

Upon the? drawings, Figs. 1 and 2 represent this lightning arresterrespectively in vertical section and in horizontal section on the lineA-A of Fig. 1. Fig. 3 is an explanatory diagram representing themagnetic blow-out field, and Fig. 4 is a diagram of the capacitances andresistances which operate in controlling the voltage distribution.

In Figs. 1 and 2, there is illustrated a container I made ofinsulatingmaterial, closed tightly by a metallic cover 2 carrying theterminal 3, connected to the voltage line. Thebottom of the containerisclosed tightly by suitable elements 4 and 5 which are connected toground bythe conductor 6 and which may serve at the sametime assupporting means.

The closure plate 4 supports a stack of special resistances 1 made ofvalve-type material the ohmic value of which decreases according to asuitable law when-the applied voltageincreases; the centering'of thesespecial resistance maybe effected in' any suitable manner, for-example,by insulating blocks 8.

This stack issurmounted by a certain number of. metallic disks 9A, 93,etc., of which only two are shown, separated by insulating spacers Illand centered in any suitable manner, for example as represented, bycut-out and bent tongues II. The disk 9A carries upon a metallic pillar12 a fixed electrode l3 of the first spark gap, while the disk 93carries by the'intermediary of a bolt I4 theother electrode l5of thesame first spark gap, which electrode co-operates with the electrode [3,the parts 13 and lt'having the'shape of horns. The electrode I5 is madeadjustable'for varying the length of the spark gap, adjustability beingprovided by any. suitable and well-known expedient.

To the disks 9A and 93 there are attached in any suitable manner pairsof pole-pieces l5 and I! made of magnetic metal, the shape of whichisseen in plan in Fig. 2 and in detail in Fig. 3. It is seenthat the pairof pole-pieces It comprises a common yoke EBA, curved in shape andarranged near. to the respective electrodev and at right anglesto thepath of the arcfburning between the two electrodes l3and H5. The pair ofpole-pieces I'I similarly-comprises a common yoke I IA. The disks QAand9B likewise carry pairsof armatures having the form of sectors [8 and iswhich are maintained in position in' any suitable manner, as'by benttongues 24' (see Fig. 2). These-sectors are made'of a semi-conductivematerial having a relatively high resistance, such for-example as a 3synthetic resin comprising a small quantity of conductive materialdispersed therein.

The upper face of the disk 9B carries, at a position opposite to that ofthe adjustable electrode [5, a fixed electrode 20 similar to theelectrode l3, and two sectors (not shown) similar to H3 and IS; theupper disks 9C, etc. are arranged in like manner, so that, in the casewhere the lightning arrester comprises for example five spark gaps inseries, there are six disks 9A, 9B, 90, etc., and correspondingresistance sectors I8 and I9. It is thus seen that the spark gaps arelocated alternately to right and left of the vertical axis, so that thepath of the discharge current forms a series of loops. This assemblypresents the overall shape indicated diagrammatically by the chain line2| it is maintained in place by a spring 22 and a contact 23.

In the operation of the device, an arc which strikes at a in Fig. 3,produces a magnetic field of which the lines of force pass initiallyalong the chain lines shown; it will be understood that this field,which tends to present a minimum reluctance and to shift towards theyoke ISA, exerts upon the are at a a thrust in the direction of thearrow F. This thrust obviously reinforces the magnetic blow-out actionproduced by the current loops mentioned above, so that the areimmediately leaves its starting position, effectually deionizing andpreserving the striking zone voltage distribution which will beexplained hereinafter, the number of spark gaps in series can be reducedto a minimum, which simplifies construction and limits the over-allsize. It is thus seen that the above-mentioned conditions 1, 2 and 4,relating to high breaking power, absence of considerable erosion andsimplicity of construction, are in fact fulfilled.

As regards the condition 3, relative to striking and breaking voltages,reference will be made to Fig. 4, which represents a simplifiedelectrical diagram of the improved lightning arrester, on thesupposition by way of example that it comprises four gaps in series.

The capacitances between the adjacent surfaces of the sectors I8 and 19of each pair of contiguous disks 9A, 9B, etc. are shown at Cs; the ohmicresistances of these sectors are designated as r. The whole series orchain shown is connected between the high-tension line L and theresistance R, representing the stack of elements 1 shown in Fig. 1, thelower extremity of this resistance R being connected to ground.

The references Ce represent the capacitances between the electrodes ofthe various spark gaps such as iii-l5, but, according to the invention,the capacitances C are much greater than the capacitances Ce of whichthe function is negligible in practice. The by-pass condensers Cd1 toCda correspond to the capacitances of the disks 9A, 93, etc., with alltheir fittings in relation to ground, these being much smaller than Cs.

It can be seen from this diagram that there is no permanent conductivepath between the line L and the ground, so that normally no leakagecurrent exists and the device cannot develop any undesirable ordangerous heating effects.

Supposing, to give a definite example, that the capacitance CS is of theorder of 10 micro-microfarads, the capacitative impedance of Cs for theindustrial frequency of cycles per second is of the order of 3.10 ohms,and if the resistance 'r is of the order of a few megohms, thedistribution of the voltages which appear upon the capacitances Ce ofthe spark gaps becomes practically uniform, for, at low frequencies, itis essentially determined by the capacitances Cs which then play adominant part.

On the contrary, at surge frequencies of the order of 10,000 cycles persecond, for example, the capacitative impedances of C5 become of thesame order as the resistances 1', and at surge frequencies of the orderof 100,000 cycles per second (corresponding to the wavefronts producedby lightning) they become negligible.

In these conditions, the capacitative current at high frequency (or asteep-fronted surge) which traverses the chain of condensers C5,neglecting all the by-passes, is limited and determined by theresistances 1.

But if, according to a particular feature of the invention, theresistances are then of the same order as, if not higher than thecapacitative bypass impedances Cdl to Cd5, the currents which passthrough these last have values which become greater and greater inproportion as the frequency increases. It follows that for increasingfrequencies, the distribution of the voltages between the spark gaps Cebecomes more and more non-uniform and consequently that the strikingvoltage of the arrester is lowered more and more.

It is seen, therefore, that due to the described combination ofappropriate capacitances and resistances, suitably connected in series,and bypass capacities, there is obtained at industrial frequencies auniform distribution of the line voltage.

These preferred means may be associated with the magnetic blow-outdescribed above, which improves substantially the deionizing propertiesof the spark gaps; these last present an increased breaking voltagewhich allows of operating them under relatively high working voltage,while the uniform distribution of voltage ensures their methodical andrational utilization. These two characteristics allow therefore ofreducing to a minimum the number of spark gaps in series.

The effectiveness of the deionization of the arcing or spark gapspresents 11 rev-rise the advantage of rendering the breaking voltagevery close to the striking voltage; the latter can therefore be selectedas low as desired per spark gap. Since, moreover, the distribution ofvoltage over the spark gaps is practically independent of externalinfluences, there is no need at all for providing a wide margin ofsafety in the adjust ment; this margin can be selected as narrow asdesired.

Lastly, under steep-fronted surge waves, the striking voltage issubstantially lowered (surge factor lower than unity), which is anadvantageous characteristic, as well known.

The condition 3 mentioned above is likewise fulfilled, and it is to benoted that this result is attained without onerous complications, norweakening of service security, as is necessarily involved, for example,by the use of shunting resistances, such as are, in certain knownapparatus, permanently traversed by ohmic currents of a value by nomeans negligible.

It is to be noted that the embodiment described can be modified invarious ways without departing from the scope of the present invention.For example, it is possible to increase at will the by-passcapacitances, as well as the capacitances in series; this allows ofmaintaining the uniform distribution of voltage between spark gaps atindustrial frequency, and of obtainin a more unequal distribution athigh frequency, that is to say lowering in a still greater proportionthe corresponding striking voltage.

For this purpose, it is possible in particular to arrange the disks 9A,9B, 90, etc. in the lower part of the apparatus, below the resistances1, instead of placing them in the upper part, or else to alternate theresistance blocks 1 and the said disks.

It is likewise possible to metallize a suitable part of the externalsurface of the insulating casing I so as to increase the capacitances Cdin relation to earth.

What I claim is:

1. In a lightning arrester of the type having a resistance of valve-typematerial connected in series with a plurality of spark gaps shunted byvoltage-distributing by-pass capacitances, a series-gap structurecomprising a stack of superposed and substantially coaxial metal discsadapted to furnish part of said voltage-distributing capacitances, eachintermediate disc of said stack carrying an arc electrode upon one faceand another are electrode in a diametrically opposed position on theother face, and each extreme disc of said stack carrying a single arcelectrode upon its face adjacent to the next intermediate disc and inclosely spaced relation to the electrode upon the adjacent face of saidnext intermediate disc, all said electrodes having the form of horns,and the combination of all said electrodes providing a plurality ofspark gaps located alternately at diametrically opposite positions andinterconnected in series by relatively long current loops adapted toproduce magnetic blow-out fields for the arcs at said spark gaps, withmeans for reinforcing the action of said blow-out fields, saidreinforcing means comprising magnetic pole-pieces carried by said discsin the vicinity of the respective electrodes and provided with yokesextending radially outside of said stack and at right angles to the arcpaths between said electrodes, the magnetic fields induced between saidpole-pieces by the arcs between said electrodes operating to force saidarcs away from the axis of said stack.

2. In a lightning arrester of the type having a valve-type resistance inseries with a plurality of magnetically blown spark gaps shunted byvoltage-distributing by-pass capacitances, a seriesgap structurecomprising a stack of superposed insulated metal discs adapted tofurnish part of said voltage-distributing capacitances, eachintermediate disc of said stack carrying a horn-like arc electrode uponone face and a horn-like arc electrode in a diametrically opposedposition on the other face, and each extreme disc of the stack carryingupon its face adjacent to the next intermediate disc a single horn-likeare electrode in closely spaced relation to the electrode upon theadjacent face of said next intermediate disc, the combination of allsaid electrodes providing a plurality of spark gaps located alternatelyat opposite sides of said stack and connected in series by relativelylong current loops whereby at each spark gap a magnetic blow-out fieldfor the are at said spark gap is produced, said series-gap structurebeing combined with means for increasing the action of said blow-outfields, comprising upon each electrode a pair of magnetic pole-piecesattached to said discs, each pair of said polepieces being provided witha common yoke arranged near to the respective electrode and at rightangles to the arc path at said electrode, and each yoke being locatedexternally of said stack in order to shift the discharge are in the samedirection as the magnetic blow-out action due to said current loops,whereby a double blow-out effect is obtained.

3. In a lightning arrester according to claim 2, means for selectivelycontrolling the voltage distribution across the spark gaps as a functionof the surge frequencies but Without producing leakage currents,comprising additional capacitor arniatures made of resistivesemi-conductive material and forming spaced projections upon adjacentmetal discs, whereby capacitive surge currents flowing between saidarmatures are controlled by the resistance of said semi-conductivematerial, and the spacing apart of said armatures prevents theestablishment of a permanent conductive path between the line and theground.

4. In a lightning arrester according to claim 2, means for selectivelycontrolling the voltage distribution across the spark gaps according tothe surge frequencies but without producing leakage currents, comprisingadditional resistive capacitors formed by co-operating armatures of ahighly resistive semi-conductive material forming opposed projectionscarried in spaced relation by adjacent metal discs, capacitive surgecurrents flowing between said armatures being controlled by theresistance of said semi-conductive material, the spacing apart of saidarmatures preventing the establishment of a permanent conductive pathbetween the line and the ground, and the values of all capacities andresistances of the said series-gap structure having such a relationshipthat at low frequencies the voltage distribution is substantiallyregular, while at high surge fre-' quencies it is non-uniform,wherebythe striking voltage is lowered.

5. In a lightning arrester according to claim 2, means for selectivelycontrolling the voltage distribution across said spark gaps as afunction of the surge frequencies but without producing leakagecurrents, comprising additional resistive capacitors formed by suitablyspaced armatures of a resistive semi-conductive material, said armaturesbeing carried by adjacent metal discs and spaced apart at such distancesthat their capacitative impedances at high surge frequencies are of thesame order as their resistances, whereby large capacitative currents areessentially controlled by the resistance of said resistive material, andthe spacing apart of said armatures prevents the establishment of apermanent leakage path between the line and the ground.

STANISLAS TESZNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 701,577 Klein June 3, 19021,902,510 McEachron et a1. Mar. 10, 1933 2,151,559 McEachron Mar. 21,1939 2,179,297 Johnson Nov. 7, 1939 2,324,108 Pyk July 13, 19432,356,039 Ellis Aug. 15, 1944 2,422,978 Olsen June 24, 1947 FOREIGNPATENTS Number Country Date 560,306 Great Britain Mar. 29, 1944

